Riddle: I have three envelopes, into one of them I put a $20 note. I lay the envelopes out on a table in front of me and allow you to pick one envelope. You hold but do not open this envelope. I then take one of the envelopes from the table, demonstrate to you that it was empty, screw it up and throw it away. The question is would you rather stick with the envelope you have selected or exchange it for the one on the table. Why? What would be the expected value to you of the exchange?
Answer: The answer might seem a little counter intuitive at first but we'll see... The short answer is that it is in your advantage to exchange. But why? Well initially there was a 1/3 chance that you were holding the envelope with the note in it and a 2/3 chance that the note was on the table. This is still the case after one of the envelopes on the table has been removed, there is still a 1/3 chance that you have the note and a 2/3 chance of it being on the table. If this is confusing then it may help to think that the questioner knows which envelope the $20 note is in, though in practice it doesn't actually matter. The questioner would always be able to demonstrate that the note was not in one of the envelopes on the table regardless of where the note was, so the fact that he was able to do this changes nothing. Consider a different example.... Say there are a 1000 envelopes on the table, 1 with a note inside. You pick 1 envelope, the chance that this has the note in it is clearly 1/1000, where as the chance that it is still on the table is 999/1000. Odds are its on the table. Now the questioner could, assuming he can remember where the note is demonstrate to you that the note is not in 998 of the envelopes on the table. In this case nothing would have happened to change the fact that there is only a 1/1000 chance of you having the note. That is why you exchange. What is the value of the exchange? Simply before the exchange you have 1/3 of $20 and afterwards you will have 2/3 of $20, ie the advantage to you is about $6.66
the envelopes Riddle Meme with riddle and answer link.
Riddle: An old parchment describes the location of buried treasure: "On the island there are only two trees, A and B, and the remains of a gallows. Start at the gallows and count the steps required to walk in a straight line to tree A. At the tree turn 90 degrees to the left and then walk forward the same number of steps. At the point where you top drive a spike into the ground. Now return to the gallows and walk in a straight line, counting your steps, to tree B. When you reach the tree, turn 90 degrees to the right and take the same number of steps forward, placing another spike at the point where you stop. Dig at the point exactly halfway between the spikes and you will find the treasure." However, our hero when he gets to the island finds the gallows missing. Is there any way he can still get to the treasure?
Answer: A simple experiment with a ruler and paper shows that any position for the gallows leads to the same point.
Buried Treasure Riddle Meme with riddle and answer link.
Riddle: A man buys a rope from a woman for $3.00 and hands the woman a $10 bill. The woman goes into the grocery store next door to get change. She returns and gives the man $7.00. After the man leaves, the clerk from the store comes and says, "Hey, that was a counterfeit bill you gave me." The woman gives the clerk a good bill.
How much has the woman lost?
Answer: Seven dollars plus the rope.
Counterfeit Bill Riddle Meme with riddle and answer link.
Riddle: Three cars had driven into a parking lot at the same time, and the three drivers left them all for the attendant to park. Unfortunately, he isn't too good at remembering exactly which driver drove which car. However, he is sure of these 6 facts: a. Colin drove the BMW if and only if Mr. Cooper drove the Avenger. b. Alan drove the Cortina if and only if Mr. Cooper drove the BMW. c. Colin is Mr. Brown if and only if Mr. Andrews drove the BMW. d. Brian is Mr. Andrews if and only if Colin drove the BMW. e. Mr. Cooper drove the Avenger if and only if Alan is Mr. Brown. f. Colin is Mr. Brown if and only if Alan drove the Cortina. Who arrived with which car?
Answer: Brian Brown drove the BMW, Alan Andrew drove the Avenger, and Colin Cooper drove the Cortina.
Car mixup Riddle Meme with riddle and answer link.
Riddle: There is a barrel with no lid and some wine in it. "This barrel of wine is more than half full," said Curly. "No it's not," says Mo. "It's less than half full." Without any measuring implements and without removing any wine from the barrel, how can they easily determine who is correct?
Answer: Tilt the barrel until the wine barely touches the lip of the barrel. If the bottom of the barrel is visible then it is less than half full. If the barrel bottom is still completely covered by the wine, then it is more than half full.
Barrel of Wine Riddle Meme with riddle and answer link.
Riddle: A hundred stones are placed, in a straight line, a yard distant from each other. How many yards must a person walk, who undertakes to pick them up, and place them in a basket stationed one yard from the first stone?
Answer: In solving this question it is clear that to pick up the first stone and put it into the basket, the person must walk two yards, one in going for the stone and another in returning with it; that for the second stone he must walk four yards, and so on increasing by two as far as the hundredth, when he must walk two hundred yards, so that the sum total will be the product of 202 multiplied by 50, or 10,100 yards. If any one does not see why we multiply 202 by 50 in getting the answer, we refer him to his arithmetic.
A hundred stones Riddle Meme with riddle and answer link.
Riddle: A hiker comes to a fork in the road and doesn't know which way to go to reach his destination. There are two men at the fork, one of whom always tells the truth while the other always lies. The hiker doesn't know which is which, though. He may ask one of the men only one question to find his way. Which man does he ask, and what is the question?
Answer: Either man should be asked the following question: "If I were to ask you if this is the way I should go, would you say yes?" While asking the question, the hiker should be pointing at either of the directions going from the fork.
Fork In the Road Riddle Riddle Meme with riddle and answer link.
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